JP2011089987A - X-ray diffraction and fluorescence - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a smaller device particularly more easy to use, which is capable of utilizing for both the XRD and the XRF. <P>SOLUTION: The instrument with function of both the X-ray diffraction (XRD) and the X-ray fluorescence (XRF) measurement deploys an X-ray source 10 generating the incident X-ray beam aiming at samples on a sample stand. For the energy dispersive XRD of high energy, an X-ray detection system is mounted at a place of a fixed angle of 2θ. For the XRF, the X-ray detection system is utilized. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an apparatus for both energy dispersive X-ray diffraction and X-ray fluorescence and a method of operating the apparatus.

  X-ray diffraction (XRD) and X-ray fluorescence (XRF) are two well-known methods for probing the structure and elemental composition of a sample. In general, equipment is designed to perform either one or the other.

  However, some applications have proposed instruments that perform both X-ray diffraction and X-ray fluorescence.

  For example, US5,745,543 describes the problem of low X-ray power reaching the XRF detector, a line focus source that enables XRD measurement, a planar or cylindrical analytical crystal and a position sensitive detector in the fluorescence measurement section. We are proposing devices that can be overcome by using them together. Therefore, a collimating system that reduces the strength is not used.

  Another proposal is made by WO2008 / 107108. This includes useful discussion about the difficulties that can be experienced when trying to combine XRD and XRF. In particular, the discussion highlights the difficulty of placing an X-ray detector that can be moved over a wide angular range for XRD and close to the sample for XRF. The intensity / sensitivity of each technique is optimized using a specific source for each.

G. Harding, X-ray scatter tomography for explosives detection ", Radiation Physics and Chemistry volume 71 (2004), pp.869-881

  Thus, a smaller device with more or less normal design that can be used for both XRD and XRF, especially easier to use, including all, some or none of the following characteristics: There remains a need for what can be incorporated into research institutes such as production lines, manufacturing plants and universities without requiring the handling of complex samples.

  The inventors have realized that the use of energy dispersive XRD is particularly suitable for combination with XRF, and thus for composite devices running both XRD and XRF.

  Preferably, the energy range used includes high energy X-rays greater than 10 keV, preferably greater than 20 keV. The use of a high energy energy dispersive (HEED) XRD is particularly preferred as it allows good particle statistics. This can be done by using XRF tube continuous band radiation for XRD, rather than the characteristic line used for XRF tube XRF. Characteristic lines suitable for XRF can be in the range of just below 3 keV (enhance elements with a small atomic number Z) and around 20 keV (enhance medium range elements). Using 2.6 keV L-lines for XRD (eg Rh L-lines) results in very poor penetration depth and therefore poor particle statistics. Instead, using continuous-band radiation of such tubes for diffraction allows measurements in a suitable energy range, depending on the sample matrix.

  For a better understanding of the present invention, embodiments will now be described, purely by way of example, with reference to the accompanying drawings.

1 shows an apparatus according to the present invention. It is a figure which shows the result obtained about the cement sample.

  Referring to FIG. 1, an apparatus according to the invention is for mounting a housing 2 and a sample, which may be evacuated or gas-filled (He) in the case of wet / liquid samples. A sample holder 4 is included. The sample holder may be adapted to hold a specific type of sample, in this example cement. The sample holder 4 extends in the lateral direction in a direction called a sample surface 6 indicated by a dotted line.

  The X-ray source 10 is provided on one side of the sample surface in alignment with a beam adjustment system 12 that collimates X-rays to form an X-ray beam in the incident X-ray direction 16. The X-ray source 10 is a source of both white X-rays, that is, X-rays having a certain range of wavelengths and characteristic lines.

  Further details are discussed below. The X-ray source is mounted on the X-ray port 14 in the housing. Since this port is for mounting an X-ray source, it is referred to as an X-ray source port 14.

  In order to mount the X-ray detection system 22, an X-ray port 20 is provided at an angle of 2θ, in this example, on the opposite side of the sample surface with respect to the X-ray source. This X-ray detection system 22 is intended for energy dispersive X-ray diffraction measurements, so the X-ray port is referred to as the XRD port 20 and the X-ray detection system is referred to as the XRD detection system 22. A beam conditioning system 24 for collimating the beam is provided in front of the XRD port 20 to obtain a beam to the XRD detection system 22.

  In typical X-ray diffraction, the intensity of the diffracted X-ray having the same energy as the incident X-ray is measured as a function of the angle 2θ to determine the structure of the sample. The relationship between the angle 2θ, the probed length scale d and the wavelength λ is given by the well-known Bragg equation nλ = 2dsinθ.

  In contrast, in energy dispersive (ED) X-ray diffraction, a fixed angle 2θ is used, and the variable amount is energy. Energy dispersive diffraction can be performed by using the relationship between energy and wavelength λ = hc / E in combination with Bragg's law. Thus, by measuring with a large number of energies, instead of changing 2θ while fixing the wavelength λ, the angle 2θ is fixed and the wavelength λ is changed. Thus, the XRD detection system 22 is an energy dispersive detector in the simplest design.

  This technique is actually very unusual, especially in high precision applications, but is proposed by Non-Patent Document 1 for explosives detection.

  The inventors have realized that this very unusual approach for XRD is particularly suitable for combination with XRF applications.

  In order to mount a further detection system 32, a further port 30 is provided. Since it is for XRF in this case, this port is called XRF port 30 and detection system 32 is called XRF detection system 32. The port 30 is on the same side of the sample surface 6 as the source port 14. XRF ports can be chosen to be located for transmission or reflection. The use of transmission is useful for elements with higher atomic numbers, but for elements with lower atomic numbers, the XRF port is located on the same side of the source port 14 and the sample surface 6 as shown. .

  Since XRF measurements are relatively common, we will not give a very detailed explanation of XRF measurements. Very unusual is the ED XRD measurement.

  As can be seen from the above description, the source may be a source of x-rays at multiple energies. For energy dispersive XRD, “white” x-ray radiation, ie continuous spectrum x-ray radiation, is required. In contrast, typical tubes for XRD use extremely monochromatic X-rays (eg from characteristic lines) or use a monochromator to generate such monochromatic X-rays. . Thus, if only XRD is considered, the X-ray source 10 for energy dispersive XRD would preferably use a metal target for the electron beam. Here, the metal target 18 is made of a metal having a large atomic number, for example. This is because the intensity of the continuous band increases with the target atomic number. Suitable targets include substances such as Ta, W, ... Au.

  However, the requirements for XRF are different. For XRF, it is preferable to use a source with discrete lines. Typically, the metal target 18 is made of a material selected to provide a characteristic line to enhance small and medium elements with atomic number Z. Substances such as Mo, Rh, ... Ag give characteristic lines in the low energy range and in the 20keV range. Since these materials already have slightly higher atomic numbers, their white radiation is also suitable for use in ED XRD. If the correct 2θ angle is selected, interference with characteristic lines and diffraction lines can be avoided.

  Thus, in the apparatus according to this embodiment, a substance having an atomic number of 42 to 46, such as Mo, Rh or Ag, is particularly preferred.

  Ultimately, an advantage of the present invention is that no angle meter or moving parts are required, only one X-ray source and two X-ray detectors are mounted on the port in a fixed position. As a result, an X-ray apparatus having both XRD and XRF functions can be obtained at a reasonable cost.

  The device may be adapted for a particular sample, especially in a particular industry. For example, in the cement industry, it may be necessary to measure the amount of free lime, which has a peak corresponding to a specific value of d. Thus, the exact fixed angle 2θ for a given instrument will depend on the intended sample, and so is the value of d. However, a typical angle 2θ in the range of 5 ° to 12 ° or even 20 ° is generally preferred. Bragg's law nλ = 2dsinθ gives a suitable value of θ, and therefore 2θ, when the energy range is known, and hence when the range of energy (not wavelength λ) is also known.

  However, for measuring pharmaceutical samples, the length scale d may be much larger, in which case 2θ needs to be smaller. Therefore, an angle 2θ in the range of 0.1 ° to 5 ° is preferred for measuring such samples. Thus, overall, the value of 2θ may be from 0.1 ° to 20 °, preferably depending on the intended application, preferably in a narrower range 5 ° to 12 ° or 0.1 ° to 5 °, preferably It may be in the range of 0.1 ° to 1 °.

  In use, a sample is mounted on a sample stage, X-rays are directed at the sample, and X-ray spectra are measured by both XRD detection system 22 and XRF detection system 32.

  In one example, a sample of cement having a thickness of 3 mm to 4 mm was measured. The angle 2θ was 10.1 ° in this example. FIG. 2 shows the results from the XRD detector at various energies. The peak of most interest for the cement test is the free lime peak at d = .245 nm (hence 28 keV, 2θ = 10.1 °). This is clearly visible and marked.

  It can be seen that good XRD results can be achieved even with this unusual configuration.

  The detection system may typically be an energy dispersive system as described above. In such an approach, the device can have no moving parts, in particular no goniometer.

  However, in alternative embodiments, the detection system may have chromatic dispersion elements such as crystals, goniometers and conventional X-ray detectors. These may be combined in an integrated detection system that can be mounted on the appropriate port.

  In one alternative, the goniometer may be omitted and a single position insensitive detector may be used.

  Another approach uses position sensitive detectors in combination with such chromatic dispersion elements. Thereby, the detection system uses the combination to measure the X-ray intensity as a function of energy.

  The embodiments described above include a single XRD port and a single XRF port, but to allow the XRD detection system and the XRF detection system to be moved to different angles or to allow multiple measurements simultaneously. Note that the housing may have additional ports. In particular, it may be advantageous to have multiple XRF detection systems to simultaneously measure XRF radiation in different energy ranges. In some cases, some of these XRF ports may be mounted on the opposite side of the sample surface relative to the X-ray source, ie on the same side as the XRD port.

  Furthermore, some embodiments may have one or more XRD ports. For example, for different applications as described above, there may be one XRD port at an angle 2θ in the range of 5 ° to 12 ° and one XRD port in the range of 0.1 ° to 5 °.

  Furthermore, the above embodiments have been described with reference to an x-ray source and detection system secured to a port. However, in some cases, the instrument may be supplied with just a bare port, without a source and detector.

2 Case 4 Sample holder 6 Sample surface 10 X-ray source 12 Beam adjustment system 14 X-ray port (X-ray source port)
16 Incident X-ray direction 18 Metal target 20 X-ray port (XRD port)
22 X-ray detection system (XRD [X-ray diffraction] detection system)
24 Beam adjustment system 32 Further detection system (XRF [fluorescence X-ray analysis] detection system)
30 Additional ports (XRF ports)

Claims (15)

A combined X-ray diffraction XRD and X-ray fluorescence XRF instrument comprising:
An X-ray source that provides radiation simultaneously over a continuous wavelength range, the radiation comprising a plurality of characteristic lines;
A beam conditioning system configured to define an incident X-ray beam in a diffractive surface in the direction of the incident beam;
A sample holder configured to hold a sample in an incident x-ray beam and defining a sample surface;
An XRF port positioned to measure X-rays emanating from the sample using an X-ray detection system mounted on the port for performing fluorescence analysis;
An XRD port arranged at a fixed 2θ angle in the range of 0.1 ° to 20 ° with respect to the incident beam direction for measuring diffracted X-rays;
A beam conditioning system positioned in alignment with the XRD port to select diffracted X-rays having an angle 2θ with respect to the incident beam direction;
apparatus.   The combined X-ray diffraction and X-ray fluorescence apparatus according to claim 1, wherein the X-ray source is adapted to provide X-rays at least 10 keV wide and over a range of wavelengths extending above 10 keV. apparatus.   The combined X-ray diffraction and X-ray fluorescence device according to claim 1 or 2, wherein the fixed angle 2θ is in the range of 5 ° to 12 °.   The combined X-ray diffraction and X-ray fluorescence device according to claim 1 or 2, wherein the fixed angle 2θ is in the range of 0.1 ° to 5 °.   5. A combined X-ray diffraction and X-ray fluorescence apparatus according to any one of claims 1 to 4, wherein the energy dispersive XRD detection system is mounted on the XRD port, and is mounted on the XRF port. An apparatus having an energy dispersive XRF detection system.   6. A combined X-ray diffraction and X-ray fluorescence device according to claim 5, wherein the XRD detection system comprises a goniometer, at least one crystal and at least one detector.   6. A combined X-ray diffraction and X-ray fluorescence device according to claim 5, wherein the XRD detection system comprises a wavelength dispersive element and a detector.   8. A combined X-ray diffraction and X-ray fluorescence device according to claim 7, wherein the detector is a position sensitive detector.   6. A combined X-ray diffraction and X-ray fluorescence device according to claim 5, wherein the XRD detection system comprises an energy selective detector tunable to detect energy at a selected energy.   10. A combined X-ray diffraction and X-ray fluorescence device according to any one of claims 1-9, comprising a plurality of XRF ports.   11. A combined X-ray diffraction and X-ray fluorescence device according to any one of claims 1 to 10, comprising a plurality of XRD ports, the XRF detection system comprising an angle meter, at least one crystal and at least A device having one detector.   12. A combined X-ray diffraction and X-ray fluorescence device according to any one of the preceding claims, comprising a plurality of XRD ports. A method of operating a combined X-ray diffraction and X-ray fluorescence apparatus having an X-ray source, beam conditioning system, sample holder, X-ray fluorescence (XRF) port and X-ray diffraction (XRD) port:
Mounting a sample on the sample holder;
Providing radiation from the x-ray source simultaneously over a continuous wavelength range, the radiation comprising a plurality of characteristic lines;
Defining an incident X-ray beam incident on the sample in the direction of the incident beam in the diffractive surface;
Measuring X-rays at the XRF port for fluorescence analysis;
Selecting diffracted X-rays having a fixed 2θ angle with respect to the incident beam direction;
Measuring the intensity of selected diffracted X-rays as a function of energy,
Method.   14. The method of claim 13, comprising providing x-rays from the x-ray source over a range of wavelengths extending at least 10 keV and above 10 keV.   The method according to claim 13 or 14, wherein the fixed angle 2θ is in the range of 5 ° to 12 ° and / or in the range of 0.1 ° to 5 °.

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